Issue #13959: Rename imp to _imp and add Lib/imp.py and begin

rewriting functionality in pure Python.

To start, imp.new_module() has been rewritten in pure Python, put into
importlib (privately) and then publicly exposed in imp.

Lib/imp.py

@@ -0,0 +1,22 @@
+"""This module provides the components needed to build your own __import__
+function.  Undocumented functions are obsolete.
+
+In most cases it is preferred you consider using the importlib module's
+functionality over this module.
+
+"""
+# (Probably) need to stay in _imp
+from _imp import (lock_held, acquire_lock, release_lock, reload,
+                  get_frozen_object, is_frozen_package, init_builtin,
+                  init_frozen, is_builtin, is_frozen, _fix_co_filename)
+# Can (probably) move to importlib
+from _imp import (get_magic, get_tag, get_suffixes, cache_from_source,
+                  source_from_cache)
+# Should be re-implemented here (and mostly deprecated)
+from _imp import (find_module, load_module, load_compiled, load_dynamic,
+                  load_package, load_source, NullImporter,
+                  SEARCH_ERROR, PY_SOURCE, PY_COMPILED, C_EXTENSION,
+                  PY_RESOURCE, PKG_DIRECTORY, C_BUILTIN, PY_FROZEN,
+                  PY_CODERESOURCE, IMP_HOOK)
+
+from importlib._bootstrap import _new_module as new_module